Motor vehicles are increasingly being fitted with systems for monitoring and/or measuring parameters, comprising sensors.
By way of example of such systems, mention may be made of the tire pressure monitoring systems that comprise electronic modules mounted on each of the wheels of vehicles, these being dedicated to measuring parameters, such as pressure and/or temperature of the tires with which these wheels are fitted, and intended to inform the driver of any abnormal variation in the measured parameter.
One of the current solutions most commonly used for attaching the electronic modules to the wheel rims is to make electronic units each made up of an electronic module assembled with an inflation valve that allows said electronic module to be secured to the rim of the wheel.
One solution regarding such electronic units is to produce special-purpose inflation valves designed for transmitting the loads to which the electronic modules are subjected. However, this solution proves expensive because, in addition to the high price of the inflation valves, which are generally all-metal, it entails the production of ancillary components (nuts, seals, . . . ) which are especially designed to ensure airtight attachment of the inflation valves to the rims.
With a view to alleviating this disadvantage, a second solution is to produce inflation valves made of elastomer material, having the same basic design as the conventional “snap-in” inflation valves, but modified in order to be able to absorb the forces to which the electronic modules are subjected.
This solution has notably resulted in the creation of an electronic unit comprising:                an electronic module,        an inflation valve of the “snap-in” type, comprising:                    a valve body made of an elastomer material, provided with a longitudinal axial bore and intended to extend through an orifice made in the rim, said valve body being made up of an elastically deformable trunk and of an abutment head for butting against the rim, which head is separated from the trunk by a neck designed to become positioned in airtight manner in the orifice made in said rim,            and a hollow tubular core made of a rigid material, housing a shut-off mechanism and of dimensions suited to being housed in the bore of the valve body and to extending on each side in the continuation of said valve body, said tubular core being made up of two longitudinal portions arranged with respect to one another and relative to the valve body in such a way as to allow the trunk elastic deformation suited to allowing the inflation valve to be mounted through the orifice in the rim,                        and means of joining the electronic module and the inflation valve.        
Because of these specific features and, in practice, such an electronic unit has the advantage of guaranteeing that the inflation valve will behave in a similar way to a traditional “snap-in” type of inflation valve. In particular, this inflation valve of the “snap-in” type eliminates the need for a nut to hold the tire parameter monitoring electronic unit in position on the wheel rim on which it is mounted, and this is an advantage because it simplifies the installation of said electronic unit.
However, when the vehicle is moving at high speed, stressing forces are applied to the tire valve. These relatively high forces may lead to deformation of the body of said valve which is made of an elastomer material, and this may cause air with which the tire is inflated to escape.
These forces notably increase with the mass of the tire parameter monitoring electronic module.
The electronic modules are generally made up of a housing containing the control electronics for these electronic units. The housings generally have an elongate shape and enclose, on the one hand, a printed circuit or “PCB” comprising the control electronics for the electronic unit and, on the other hand, a battery power supply, said printed circuit and said battery being arranged in the one same plane. The disadvantage of such electronic modules is that they have a high weight giving rise to a significant imbalance phenomenon, notably when the vehicle is moving at high speed, and this leads to an appreciable reduction in the dynamic performance of such electronic units.
In order to alleviate these disadvantages, a more compact housing in which the printed circuit and the battery are arranged not coplanar but parallel, one above the other, or alternatively not coplanar but perpendicular to one another has been proposed (see notably document WO 2013153134, incorporated by reference herein). These arrangements make it possible to reduce the mass of the electronic module and, therefore, to increase the dynamic performance of the electronic units, thus reducing the stresses applied to the valve body.
However, before the tire is mounted on the wheel rim an optimization step better known as “matching” is generally carried out and involves rotating the tire on the rim in order to optimize the position of the imbalance of said tire in relation to that of the rim, before the wheel is balanced, so as to lessen the effects of irregularities in the shape of the tire and of the rim.
Now, during this operation of “matching” a tire to a rim of a wheel fitted with an electronic tire parameter monitoring unit, said tire may come into contact with the electronic unit with which said rim is fitted and, because of the compact shape of the electronic module and because of the ability of the “snap-in” valve body made of elastomer to deform, it may apply torsional and translational loadings to the electronic unit such that it is made to pivot about the longitudinal axis of the means joining the electronic module and the inflation valve together.
This defective positioning of the electronic unit leads to incorrect operation of said electronic unit. Specifically, the electronic module of the electronic unit notably comprises electronic components the operation of which is dependent on their positioning. For example, the electronic unit comprises a sensor for measuring the radial acceleration of the wheel, such as an accelerometer, the measurements of which are exploited in target applications, notably:                automatic learning by the sensors or the monitoring of the position of the sensors themselves;        location of the wheels in order to monitor the tire pressure corresponding to each wheel located,        detection of tire overload and tire wear,requiring accurate positioning of the radial acceleration sensor and, therefore, of the electronic module, with respect to the rim of the wheel.        
The electronic module of the electronic unit further comprises a radiofrequency (RF) emitter and an LF (Low Frequency) antenna, so as to be able to communicate with a central electronic unit (mounted on the vehicle) for receiving signals emitted by the emitters of each electronic module with which the wheels of said vehicle are equipped. Hence, poor positioning of the electronic module leads to poor RF communication between the electronic units with which the wheels of the vehicle are equipped and the central electronic unit of said vehicle.
In addition, this poor positioning of the electronic unit may lead to damage, such as the pulling-out of said electronic unit during operations of fitting, removing, or inflating the tire.
Thus, a pivoting of the electronic unit with respect to the rim of the wheel on which it is mounted is therefore to be avoided.
At the present time, in order to overcome this problem, it is proposed that a visual check be performed of each wheel, during the operation of “matching” the tire to the rim, in order to set aside products exhibiting an electronic unit that has pivoted. In addition, a manual intervention is needed on each defective product in order to correctly reposition the electronic unit with respect to the rim of the wheel on which it is mounted. This human intervention to check and correct the positioning of the electronic units during the operation of “matching” the tires to the rims of the wheels leads to a very significant additional cost.